To fulfill basic performance requirements as a sport bike while setting higher targets for environmental performance, a DOHC was chosen as the valve system. DOHC improves combustion efficiency by reducing the weight of the reciprocating portion of the valves. This selection also allows us to freely choose the included valve angle, the port shape, and the shape of the combustion chamber. The choice of DOHC contributes to improved product appeal as a sports bike as well as to performance. For the valve system, a roller rocker arm was adopted by a DOHC engine motorcycle for the first time in the world. A low-friction valve train with a smaller cylinder head was achieved through an ultra-compact layout for the roller rocker arm.The choice of a shim design for valve tappet adjustment reduced the rocker arm weight, while friction was reduced by setting the valve spring load to a low level.For better maintainability, the shim can be replaced without removing the camshaft.

Roller rocker arm Silent cam chain (SV chain)

To reduce blow-by gas and oil consumption, a spiny sleeve was adopted for the cylinder sleeve. Small spines have been added to the outer surface to improve cooling performance and help reduce distortion of the inner cylinder's shape. In addition, centrifugal casting allowed a thin, uniform wall thickness, which aids weight reduction. For emission measures, an O² sensor is combined with the built-in air induction (AI) system and a catalyzer is fitted inside the exhaust pipe to comply with Euro 3 emission regulation. The power unit complies with other environmental regulations such as Thailand's sixth emission standards, for which the evaporator system (evaporative emission control system) was put in place for the Thai model.

Cylinder sleeve AI/O² sensor

Catalyzer

AI pathway

In the area of engine performance, a short-stroke engine (bore stroke: Φ76 × 55) was chosen to improve responsiveness in making the bike's sporty characteristics easy to handle. The resulting bore stroke is on a par with that of CBR1000RR, Honda's high performance, super sport bike. In designing the crankshaft, no efforts were spared to reduce weight in order to lower the inertial mass while achieving additional weight reduction in the piston and connecting rod. Sufficient cooling performance was ensured by conducting a high-efficiency cooling water flow analysis based on a CAE simulation to give higher output. To ensure that output characteristics are stress-free and powerful from low to high rpm ranges, charging efficiency was improved. Additional measures for higher efficiency include straightening from the air cleaner to the exhaust pipe. Valve stems have been made thinner, although valve diameters are large for both intake and exhaust. This valve design is coupled with a wide opening angle and a high-lift cam to improve intake/exhaust efficiency. To achieve output characteristics that are easy to handle at low speed and smooth rev-up at high rpm, the intake/exhaust systems were thoroughly analyzed to adopt the ideal port/pipe length and bore size.

Cross-sectional view of straight port's form

Cross-sectional view of cylinder head Valve shapes

CHASIS

The combined ABS model is equipped with a three-pot caliper in front, front/rear wheel speed sensors that detect the condition of the vehicle, and an ABS modulator with a built-in ECU. The ECU processes information from wheel speed sensors and controls the feed of hydraulic pressure to the caliper. Advanced braking performance was achieved in step with maneuverability by placing heavy items such as ABS modulator near the center of gravity of vehicle body.

Sales name CBR250RModel type Honda MC41

Overall length × Overall width × Overall height (m)

2.035 × 0.720 × 1.125

Wheelbase (m) 1.370Ground clearance (m) 0.145

Seat height (m) 0.780Curb weight (kg) 161 (STD) 165 (ABS)

Riding capacity (No. of people) 2Minimum turning radius (m) 2.5

Engine typeCS250RE, liquid-cooled 4-stroke DOHC single cylinder

Displacement (cm³) 249Bore × Stroke (mm) 76.0 × 55.0Compression ratio 10.7Fuel supply system Programmed fuel injection system (PGM-FI)

Starter type Self-starterIgnition type Full-transistor battery ignition

Lubricating type Wet sumpFuel tank capacity (L) 13

Clutch type Wet multiplate with coil springs

Transmission type Constant mesh 6-speed return

Transmission gear ratio

1-speed 3.3332-speed 2.1183-speed 1.5714-speed 1.3045-speed 1.1156-speed 0.963

Reduction gear ratio (primary, secondary) 2.808 / 2.714Caster angle/Trail (mm) 25º00´/ 95

Tire sizeFront 110/70-17M/CRear 140/70-17M/C

Brake typeFront Hydraulic diskRear Hydraulic disk

Suspension typeFront Telescopic

RearSwing arm (Pro-link suspension system)

Frame type Diamond